Face detection algorithms have many uses and have been studied extensively. For example, most existing real-time face detection systems use Haar-wavelets as visual features, because they can be evaluated in constant time at any scale using integral images comprising a data structure that allows querying the sum of all pixel values above and to the left of any location in the input image in constant time.
However, existing Haar-wavelet-based real-time face detection algorithms need relatively powerful computing devices to provide the processing power needed for most applications. Commonly used face detection algorithms take too long on contemporary mobile device hardware, and are thus not suited for real-time processing on mobile hardware.